Stem sealing machine



Nov. 9, 1943. c HAPGOOD 2,334,001

STEM SEALING MACHINE Filed Oct. 17, 1941 INVENTOR JZIULQIYWME Y W fl w) ATTORNEY Faiented Nov. 9, 1943 STEM- SEALING MACHINE I John'C. Hapgood, Chatham, N. 1., assignor to Radio Corporation oi America, a corporation of Delaware Application October 17, 1941, Serial No. 415,361

1 Claim. (CL 49-44") My invention relates tostem sealing-in machines for Joining the glass stems and bulbs of envelopes for radio tubes, lamps and the like.

The stem or glass portion of an envelope,

containing the lead-in conductors, is usually mounted on a so-called stem pin or chuck for supporting the rim or flare of. the stem inside, concentric with,'and intermediate the ends of the bulb. In the long neck method of sealing, the flarels inserted a considerable distance into the bulb and sharp fires, usually high temperature pointed gas flames, locally melt and seal the bulb to the flare, whereupon the neck portion of the bulbor cullet below the seal is cut off by the fires. When the glass for holding the bulb and stem, as in the conventional glass working lathe.

The particular stem shown here comprises a dish-shaped header with thelead-in conduc tor 4 sealed in the bottom of the cup. The stem I is setinto athin' walled tapered metal cup 5 is of the high melting type and is relatively large andthick, diillculty is experienced in making good -seals in'reasonably short periods of time. The bulb walls are often thinned above the seal and incomplete seals or holes may appear bet'ween'the flare and the bulb. 1

An object of my invention is a sealing-in ma-' chine for joining bulbs and stems of en-.

velopes in which the seal maybe strong and vacuum-tight. I v g A further object of my invention is a sealing-in machine that will consistently make good bulb-to-stem seals and that is fast and easy to'operate.

The characteristic features of my invention are defined in the appended claim and one embodiment thereof is described in the following sleeves l2 to insure smooth vertical movement with the rim 6 of the stem protruding slightly over the rim of the cup. The bulb islowered over the stem and its assembled electrodes to bring the bulb to rest upon the transverse horizontal platform 1 which extends across the bulb holder; Parallel bulb holder posts 8, supported on the spindle 3, carry at their upper ends clamping jaws 9 for gripping the upper end of the bulb. According to one of the characteristic features of my invention the platform I is vertically slidable on the posts and may be held at 'will in any one of a number of predetermined parallel positions hired by the steps or notches ID on the latch ll secured to the lower end of one of the posts. The platform is held perpendicular to the axis or center of rotation of the spindle andis fixed to the ends of of the platform. In its uppermost position the platform is underneath the bulb and forms a stop on which the rim of the bulb rests and thus may be used for determining the proper vertical position. of the bulb when loaded.

Upon the application of flres the platform is dropped to a lower position determined by the first step on the latch. As shown in Figspecification and shown in the accompanying drawing in which Figure 1 is an, elevational view of my improved sealing-in machine, liigure 2 is a'sectional view of my machine taken along the dot-dash line of Figure 1, Figures 3, 4 and 5 are detailed views partly in section of the stem holder of my novel machine and show three successive steps in sealing operations performed on the machine.

The glass bulb l of the envelope, to which the glass stem or header 2 is to 'be sealed, is supported at its upper end in axial alignment with the stem and with its open end down. The stem is telescoped a considerable distance into the bulb so that sealing flames will not splash'lnto'the envelope to damage electrodes mounted on the stem. The entire sealing head assembly is preferably formed on a single rotating spindle 3 which carries the bulbv and separately iournalled chucks may be employed fstem holders so that they may be rotated as a unit in the flames. Alternatively, of course,

- ure 3; pointed flames are directed against the side of'the bulb opposite the stem flare. During this firing the platform is spaced a short distance below the-end of the bulb softhat as the bulb softens and stretches lengthwise the lower end of the bulb settles toward the platform freely and by gravity only. The bulbwall draws in and at about the time the stem and bulb join, as shown in Figure 4, the descending rim of the bulb comes to rest on the platform and the stretch of the bulb wall is interrupted by the platform. The molten glass in the seal region puddles and thickens considerably andit is found that the bulb wall above the seal region is considerably thicker when made on my machine than when made on .the conventional stem sealing machine.

The platform is finally dropped to its lowermost position, as shown in Figure 5, .and the flames now'directed to Just below the seal region, cut of! the lower bulb-portion orcullet. With a short annealing the finished envelope is removed.

I am not certain why the glass in the seal region and in the bulb wall above the seal should be thicker when made on my machine, or why holes do not appear between the bulb and stem,

but it is my belief that the retarded descent of the cullet and the interrupted stretching permits the glass in its molten state to draw by its surface tension into a thickened puddle at and above the seal. The stretch is retarded instead of accentuated, as in the usual stem machine where a positive pull 'is usually placed on the cullet, and the pull of the cullet is limited to some value less than its free gravitational pull.

Any desired number and length of steps in the downward movement of the platform may be employed. The latch may be operated manually, or automatically by triggering mechanism interlocked with the drive for the-spindle. The frequency and length of each step will of course be determined by the number of heads on the sealing machine, flre temperatures, and speed of in-- 'dexing. If desired the platform could be moved steadily downward during the sealing as with a lead screw. According to our invention of course,

the downward travel of the -platform is at a rate less than the rate of free downward travel of the bulb rim.

Particularly good results have been obtained in sealing-in envelopes of radio tubes commer cially known as the "813 having a glass bulb I and glass stem 2 substantially as shown in Figure 1 where the bulb is high melting hard glass of the type commercially known as Nonex, and having a bulb diameter of 2.5 inches and a wall thickness of .035 to .075 inch. The "813 stem also of None: glass, is about .090 to .120 inch thick at the flare-which is about 2.25 inches in diameter. A turret with six of my improved sealing heads with an indexing period oi 40 sec,-

onds consistently gives strong vacuum-tight seals using six medium hard sealing flames of commercial illuminating gas mixed with oxygen and air, the flames being about six inches long. As the bulb all softens the stretch begins and,.appatently because of the shading effect of the side posts and uneven heating, the skirt of the' bulb tends to move of! center. As the bulb rim approaches the platform it again straightens and at the instant of sealing the cullet and upper portion of the bulb are in accurate alignment. No visible irregularities in wall thickness throughout the length of the seal are noted. The cut-oi! flames are more pointed and are harder" or of a higher temperature than the sealing flames, so that the glass of the bulb below the seal, called the cullet, may be severed from the finished envelope as shown in Figure 5.

My improved sealing-in machine produces uniform strong and vacuum-tight seals, iseasy to operate, and is fast in production.

I claim: 4

A stem sealing machine comprising ,a stem holder, a cooperating bulb holder above the stem holder for carrying a bulb open end down and in axial alignment with the stem holder and in telescop'ed relation with a stem in said stem holder, and a vertically slidable horizontal platform extending transversely of said bulb. holder and movable at will from an upper position in which said platform is underneath and supports the rim of a bulb in said bulb holder to a lower parallel position spacedfrom said upper position and in which said platform arrests the downward movement of the lower portion of said bulb as said portion settles freely and by gravity only into contact with said platform.

JOHN C. HAPGOOD. 

